During film preparation, a film thickness needs to be measured to monitor the film preparation process, because the film thickness is an important parameter and can directly affect physical properties of the film. Therefore, measurement of the film thickness is very important.
Currently, existing instruments commonly used for measuring a film thickness include ellipsometer, but ellipsometer is only suitable for measuring films having a thickness within a certain range. When the film thickness exceeds the range, sensitivity of the ellipsometer will be lowered, leading to a large error in the measurement result and thus affect the measurement accuracy.